<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .nav{
            width: 100%;
            height: 50px;
            background-color: gray;
            margin-top: 40px;
        }
        .nav>div{
            /* border: 1px solid black; */
            height: 50px;
            width: 1000px;
            margin: 0 auto;
            display: flex;
            justify-content: space-around;
        }
        span{
           /* border: 1px solid black; */
           line-height: 50px;
        }
        a{
            text-decoration: none;
            color: aliceblue;
            font-weight: bold;
            transition: all 0.3s;
        }
        a:hover{
            font-size: 30px;
             
        }
    </style>
</head>
<body>
    <div class="nav">
        <div class="middle_main">
            <span class="span"><a href="#">首页</a></span>
            <span class="span"><a href="#">第一</a></span>
            <span class="span"><a href="#">第二</a></span>
            <span class="span"><a href="#">第三</a></span>
            <span class="span"><a href="#">第四</a></span>
        </div>
    </div>
    <script>
        let btn = document.querySelector('a')
        btn.addEventListener(function(){
            alert('没反应')
        })
    </script>
</body>
</html>